Pumping stages utilized in turbomolecular pumps to create high vacuum conditions are previously known to exist in many different designs, some of which incorporate a stator housing having a rotor disk embodied therein, wherein a gas passageway is defined along a tangential channel established between the rotor and stator.
Pumping stages especially designed for increasing pump operating range in terms of discharge pressure are discussed in German Patent No. 3,819,529, as well as European Patent Application No. 0,445,815, the latter being in the name of the applicant.
German Patent No. 3,819,529 discloses a vacuum pump having a rotor disk with a recessed periphery, forming radially extending steps which operate in conjunction with a stator having an annular groove for receiving the recessed periphery of the rotor disk. The juxtaposed rotor and stator form flow passages between the surfaces of the annular groove and the corresponding steps positioned on the periphery of the rotor disk. A disadvantage of this type of construction is that it provides a channel that is divided on the opposite faces of the rotor disk; thereby forcing the gas to follow a tortuous path when entering the portion of the channel below the rotor disk via the suction port, or when leaving the portion of the channel above the rotor disk through the discharge port.
European Patent Application No. 0,445,855 discloses a turbomolecular pump which utilizes, in addition to conventional axial flow pumping stages, one or more tangential flow pumping stages. These tangential flow pumping stages are positioned at the exhaust side of the pump in order to raise the exhaust pressure up to atmospheric pressure; thereby allowing the pump to discharge at higher pressures without being combined with a forepump. The use of these tangential flow pumping stages are effective in either a molecular or transient flow pressure range, and permit the raising of the outlet pressure from about 1 Pa to over 10.sup.3 Pa. A further rise of the outlet pressure, up to atmospheric pressure, has been obtained utilizing a different rotor design incorporating peripheral vanes mounted normal to the peripheral edge.
It is therefore a feature of the present invention to provide a modified geometry for a pumping stage, of the type described above, to improve gas compression performances and to further extend the operating range of turbomolecular pumps incorporating said invention.
It is a further feature of the present invention to provide a pumping stage design which can be easily incorporated in a turbomolecular pump, either alone or in cooperation with one or more similar pumping stages, thereby allowing the turbomolecular pump to discharge to higher pressures, approaching atmospheric pressure, without being teamed up to a forepump.
It is still a further feature of the present invention to provide a pumping stage design which can be manufactured easily at a low cost, as well as being easy to use and simple to maintain.